Due to the bandwidth limitations of transmission channels, there are a limited number of bits available for encoding the audio and video information associated with an audio-visual application, such as a video teleconference. Thus, many audio and video encoding techniques have been developed which attempt to encode the audio and video information with as few bits as possible while still maintaining the quality and intelligibility that are required for a given application.
There are many audio and video encoding techniques which have improved coding efficiency by removing the statistical redundancy arid perceptual irrelevancy from the audio or video signals, respectively. For example, the well-known MPEG video encoding technique, developed by the Motion Picture Experts Group, achieves significant bit rate reductions by taking advantage of the correlation between pixels in the space domain, and the correlation between image frames in the time domain.
A conventional audio-visual communication system will encode the audio signal and the sequence of image frames individually and then multiplex the two signals together for transmission over a digital channel to the receiver. Few, if any, audio-visual communication systems, however, have achieved bit rate reductions by analyzing both the audio and video signals and thereafter dynamically allocating the bits available for encoding the audio and video signals based on the perceptual significance of the audio and video information to a human observer.
Accordingly, a need exists for an audio-visual communication system that maximizes both bit rate efficiency and perceptual quality by performing an integrated bit assignment based on the perceptual significance of the audio and video information. In addition, a further need exists for an audio-visual communication system that dynamically encodes the audio signal based on the current content of the audio information.